Thanks for these. I just replaced a couple a vacuum lines that were leaking and wondered what they did. One came from the fuel pressure regulator. What does that line do? The other one was only about two inches long. A steel line came out from under the intake manifold right smack in the center and had this short vacuum line that converted into rubber only a couple of inches long and went into a T. From your diagram it looks like it might be the T that goes to the brake booster eventually. Which makes sense since I sometimes got a fault for the brake booster. Anyway replacing these took care of my lean codes and the brake booster codes.
Where do you get the diagrams? From the repair manual? I got the CD from Ross Tech that is a repair manual but it is largely worthless.
high vacuum from hose to fpr reduces fuel pressure... at idle and high vacuum=least fuel pressure. When throttle plate opens, vacuum drops and fuel pressure rises. More fuel pressure pushes more fuel for combustion.
Chipped engines can benefit from higher pressure or adjustable fpr's that can add more fuel under boost to reduce lean conditions that lead to knocking, triggering knock sensor and reducing performance.
That is interesting, as far as I understand. I have an MTM chip. Had an APR chip when I bought the car several years ago. MTM works better at elevation. I am happy with performance as is. Not interested in anything more. This helps explain why I was having problems when the engine was cold started. Had to let it idle for a minute or two or it would miss badly, with no acceleration.